Ultra-wideband communication system and method

ABSTRACT

The present invention provides systems and methods for communication between ultra-wideband (UWB) devices. In general, the UWB device may characterize the attenuation, and other characteristics of the communication environment. Using these characteristics the UWB device can adapt various communication parameters to improve the communication quality. The UWB device may use these characteristics to establish zones and sectors for communication with other UWB devices. Based on this zone and sector assignment the UWB device may select communication parameters for communication with other UWB devices. This Abstract is provided for the sole purpose of complying with the Abstract requirement rules that allow a reader to quickly ascertain the subject matter of the disclosure contained herein. This Abstract is submitted with the explicit understanding that it will not be used to interpret or to limit the scope or the meaning of the claims.

This application is a divisional application of, and claims priority to,U.S. non-provisional application Ser. No. 10/449,789, filed May 30, 2003entitled “ULTRA-WIDEBAND COMMUNICATION SYSTEM AND METHOD.”

FIELD OF THE INVENTION

The present invention relates generally to the field of wirelesscommunications, and more specifically to ultra-wideband wirelesscommunication that employs several communication parameters.

BACKGROUND OF THE INVENTION

The wireless device industry has recently seen unprecedented growth.With the growth of this industry, communication between wireless deviceshas become increasingly important. There are a number of differenttechnologies for inter-device communications. Radio Frequency (RF)technology has been the predominant technology for wireless devicecommunications. Alternatively, electro-optical devices have been used inwireless communications. Electro-optical technology suffers from lowranges and a strict need for line of sight. RF devices therefore providesignificant advantages over electro-optical devices.

Conventional RF technology employs continuous sine waves that aretransmitted with data embedded in the modulation of the sine waves'amplitude or frequency. For example, a conventional cellular phone mustoperate at a particular frequency band of a particular width in thetotal frequency spectrum. Specifically, in the United States, theFederal Communications Commission has allocated cellular phonecommunications in the 800 to 900 MHz band. Generally, cellular phoneoperators divide the allocated band into 25 MHz portions, with selectedportions transmitting cellular phone signals, and other portionsreceiving cellular phone signals.

Another type of inter-device communication technology is ultra-wideband(UWB). UWB wireless technology is fundamentally different fromconventional forms of RF technology. UWB employs a “carrier free”architecture, which does not require the use of high frequency carriergeneration hardware; carrier modulation hardware; frequency and phasediscrimination hardware or other devices employed in conventionalfrequency domain communication systems. UWB communications systems anddevices additionally benefit from the capability to measure distance andgeo-position. Generally, these UWB devices measure the time it takes fora UWB pulse, or signal to travel from one UWB device to another UWBdevice, and use the speed of light to determine the distance between UWBdevices.

However, the broad concept of using time and the speed of light todetermine distance has been employed for centuries. The first recordedattempts to establish the speed of light by the use of distance dateback to the experiments of Galileo in the 1600s. His only conclusionbased on his terrestrial experiments was that light moves very fast. In1676, Olaf Roemer was able to measure the speed of light to beapproximately 2.14×10 8 based on his assumptions of the distance betweenJupiter and the Earth. The current accepted measurement of2.9997924588×108 was obtained using laser interferometery.

In theory, a wireless ultra-wideband (UWB) communications pulse, orsignal transmitted from a source and received by a target arriveswithout any delays or distortions caused by the surrounding environment.Such an ideal environment is difficult to realize outside the vacuum ofouter space. In more practical environments and especially in urbansettings, the environment may have a substantial impact on the receptionof a UWB pulse, or signal.

Generally, the distance between communicating devices affects thequality of the communications channel. Electromagnetic radiationdissipates proportionally to distance squared. Additionally, the terrainaffects radio waves. Thus, the opportunity for multi-path, or “fading”effects generally increases with distance. There are essentially twotypes of fading in electromagnetic communications. Local multi-pathfluctuation is known as fast-fading or Raleigh fading. More distancefading effects may be caused by long term variation in average powerlevels, slow fading or log-normal fading, which is caused by movementover distances long enough to produce significant variations in thesignal path length. Multi-path reflections can also cause a signal toarrive at the receiver in multiple reflections, each at a differenttime. This is commonly referred to as delay spread. As signal strengthattenuates or decreases, the signal-to-noise ratio (SNR) degrades aswell, generally leading to increased bit-error-rates (BER).

Therefore, there exists a need for an ultra-wideband communicationsystem that provides reliable communication at a variety of distances,and in a variety of environments.

SUMMARY OF THE INVENTION

The present invention provides reliable systems and methods forcommunication between ultra-wideband (UWB) devices located a variety ofdistances from each other. One method of the present invention selectsat least one communication parameter that enables reliable communicationbetween UWB devices. This method comprises transmitting a time requestsignal from a first UWB device to a time synchronized UWB device. Thetime synchronized UWB device sends a response message to the first UWBdevice, which determines a time difference between the time of receiptof the time response message and the time of transmission containedwithin the time response message. A communication parameter is theselected, based at least on the time difference.

Another embodiment of the present invention characterizes theattenuation characteristics of the wireless medium though which the UWBdevices are transmitting. Using these characteristics the UWB devicescan adapt various communication parameters to improve the quality ofcommunications.

These and other features and advantages of the present invention will beappreciated from review of the following detailed description of theinvention, along with the accompanying figures in which like referencenumerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an illustration of different communication methods;

FIG. 2 is an illustration of two ultra-wideband pulses;

FIG. 3 is an illustration of zones and sectors established by a UWBdevice in accordance with one embodiment of the present invention;

FIG. 4 shows a time request message and an associated time responsemessage in accordance with one embodiment of the present invention;

FIG. 5 shows a distance request message and an associated distanceresponse message in accordance with one embodiment of the presentinvention;

FIG. 6 shows a BER request message and an associated BER responsemessage in accordance with one embodiment of the present invention;

FIG. 7 shows a fixed energy request message and an associated fixedenergy response message in accordance with one embodiment of the presentinvention;

FIG. 8 shows a sectorized zone system with a fixed access point inaccordance with one embodiment of the present invention;

FIG. 9 shows UWB enabled devices communicating in a sectorized zonesystem with a fixed access point in accordance with one embodiment ofthe present invention;

FIG. 10 shows a UWB enabled device communicating with other UWB enableddevices in the absence of a fixed access point in accordance with oneembodiment of the present invention; and

FIG. 11 shows spatial diversity assignment of time bins in accordancewith one embodiment of the present invention.

It will be recognized that some or all of the Figures are schematicrepresentations for purposes of illustration and do not necessarilydepict the actual relative sizes or locations of the elements shown.

DETAILED DESCRIPTION OF THE INVENTION

In the following paragraphs, the present invention will be described indetail by way of example with reference to the attached drawings.Throughout this description, the preferred embodiment and examples shownshould be considered as exemplars, rather than as limitations on thepresent invention. As used herein, the “present invention” refers to anyone of the embodiments of the invention described herein, and anyequivalents. Furthernore, reference to various feature(s) of the“present invention” throughout this document does not mean that allclaimed embodiments or methods must include the referenced feature(s).

The present invention provides reliable systems and methods forcommunication between ultra-wideband (UWB) devices located a variety ofdistances from each other. Generally, each UWB device employing themethods of the present invention may use various communicationparameters in response to different distance, power, environmental, andother conditions when communicating with each other.

One method of the present invention selects at least one communicationparameter that enables reliable communication between UWB devices. Thismethod comprises transmitting a time request signal from a UWB device toa time synchronized UWB device. The time synchronized UWB device sends aresponse message to the first UWB device, which determines a timedifference between the time of receipt of the time response message andthe time of transmission contained within the time response message. Acommunication parameter is the selected, based at least on the timedifference.

Another embodiment of the present invention characterizes theattenuation characteristics of the wireless medium though which the UWBdevices are transmitting. Using these characteristics the UWB devicescan adapt various communication parameters to improve the quality ofcommunications.

In another embodiment of the present invention, a UWB enabled wirelessdevice obtains distance information to at least one other UWB enabledwireless device. The distance information is then used to determine azone location for each UWB device. Specific communication parameters arethen employed for each zone. When communicating with other UWB enableddevices the first UWB device adapts its communication parameters inaccordance with the zone parameters.

In another embodiment of the present invention, a UWB enabled deviceobtains Received Signal Strength Indicator (RSSI) information from atleast one UWB enabled device. The first UWB device uses the RSSIinformation to derive RSSI-based zones for communication with the UWBenabled devices. Alternatively, the first UWB device may use the RSSIand distance information to characterize the communications environmentwithin the zone.

In a still further embodiment of the present invention, an access pointassigns communication frame parameters to each zone to reduce theprobability of multi-user interference.

Conventional radio frequency technology employs continuous sine wavesthat are transmitted with data embedded in the modulation of the sinewaves' amplitude or frequency. For example, a conventional cellularphone must operate at a particular frequency band of a particular widthin the total frequency spectrum. Specifically, in the United States, theFederal Communications Commission has allocated cellular phonecommunications in the 800 to 900 MHz band. Cellular phone operators use25 MHz of the allocated band to transmit cellular phone signals, andanother 25 MHz of the allocated band to receive cellular phone signals.

Another example of a conventional radio frequency technology isillustrated in FIG. 1. 802.11a, a wireless local area network (LAN)protocol, transmits radio frequency signals at a 5 GHz center frequency,with a radio frequency spread of about 5 MHz.

In contrast, a UWB pulse may have a 1.8 GHz center frequency, with afrequency spread of approximately 3.2 GHz, as shown in FIG. 2, whichillustrates two typical UWB pulses. FIG. 2 illustrates that the narrowerthe UWB pulse in time, the broader the spread of its frequency spectrum.This is because frequency is inversely proportional to the time durationof the pulse. A 600 picosecond UWB pulse may have about a 1.8 GHz centerfrequency, with a frequency spread of approximately 1.6 GHz. And a 300picosecond UWB pulse may have about a 3 GHz center frequency, with afrequency spread of approximately 3.2 GHz. Thus, UWB pulses generally donot operate within a specific frequency, as shown in FIG. 1. And becauseUWB pulses are spread across an extremely wide frequency range, UWBcommunication systems allow communications at very high data rates, suchas 100 megabits per second or greater.

Further details of UWB technology are disclosed in U.S. Pat. No.3,728,632 (in the name of Gerald F. Ross, and titled: Transmission andReception System for Generating and Receiving Base-Band Duration PulseSignals without Distortion for Short Base-Band Pulse CommunicationSystem), which is referred to and incorporated herein in its entirety bythis reference.

Also, because the UWB pulse is spread across an extremely wide frequencyrange, the power sampled at a single, or specific frequency is very low.For example, a UWB one-watt signal of one nano-second duration spreadsthe one-watt over the entire frequency occupied by the pulse. At anysingle frequency, such as a cellular phone carrier frequency, the UWBpulse power present is one nano-watt (for a frequency band of 1 GHz).This is well within the noise floor of any cellular phone system andtherefore does not interfere with the demodulation and recovery of theoriginal cellular phone signals. Generally, the multiplicity of UWBpulses are transmitted at relatively low power (when sampled at asingle, or specific frequency), for example, at less than −30 powerdecibels to −60 power decibels, which minimizes interference withconventional radio frequencies.

As described above, wireless devices communicate with Radio Frequency(RF) energy. Conventional technologies for RF communications employ RFcarrier waves. Data is modulated onto the carrier wave, amplified andtransmitted from the first RF device. A second RF wireless devicereceives the carrier wave, amplifies the wave, and demodulates the data.RF communications suffer from fading, multi-path interference, andchannel attenuation. Since RF energy strength is proportional to theinverse of the transmitted distance squared, the quality of RF wirelessdevice communication is dependent on the relative location of the RFdevices that are communicating. Atmospheric conditions, terrain, naturaland man-made objects can additionally degrade the received signalstrength of RF communications.

As is well known in the art, propagation of RF energy is stronglyinfluenced by the environment, both man-made and natural. For example,urban areas are generally dominated by large man-made structures.Suburban areas typically contain residential structures, and rural areasmay be more open, with wooded areas and the occasional man-madestructure.

One feature of the present invention is that it adapts communicationparameters to maximize the communication quality between UWB enableddevices. Thus, one assortment of communication parameters may be usedfor urban areas, another assortment for residential areas, with yetanother assortment used for rural areas. The assortment is not fixed foreach environment, rather the communication parameters used in eachenvironment may be altered, or other communication parameters may beemployed to obtain the best possible communication quality.

The distance between communicating devices is one importantcharacteristic in communications quality. There are numerous methods ofestablishing distance between communicating devices. One feature ofultra-wideband (UWB) systems is that they can determine the time ofarrival of a UWB pulse, or signal very precisely. For example, UWBsystems can determine pulse or signal time of arrival (TOA) to within200 pico-seconds. With an approximate propagation speed of 10centimeters per nano-second, this UWB system may be capable ofaccurately measuring distance to approximately 2 centimeters. As timeresolutions decrease in UWB devices, their ability to resolve distanceis further enhanced. Thus, because UWB technology can determine TOA tovery precise resolutions, accurate distances can be determined.

Co-pending U.S. patent application, Ser. No. 09/805,735, filed Mar. 13,2001, titled: MAINTAINING A GLOBAL TIME REFERENCE AMONG A GROUP OFNETWORKED DEVICES, teaches synchronization of UWB enabled devices to asingle master time reference. This application is incorporated herein inits entirety by this reference. Once the communicating UWB devices aresynchronized to the master time reference, distance measurements may bemade by any of the communicating devices. To determine distance, areceiving UWB device only needs to know the time of transmission and thetime of arrival of the UWB pulse, or signal. Since the communicating UWBdevices are synchronized to the same master time reference, thereference for the time of transmission is consistent between the UWBdevices. The time of arrival of the UWB signal is determined by thereceiving device, and contained within the UWB signal is the signal'stime of transmission. The distance between UWB devices is obtained bydetermining the difference between the transmission time and the arrivaltime, and multiplying it by the UWB signal speed. Because thetransmission time and the arrival time are both referenced to the samemaster time reference, the distance calculation will be accurate.

Another method of determining the distance between ultra-wideband (UWB)devices is disclosed in the following co-pending United States patentapplication that is herein incorporated in its entirety by thisreference: USE OF THIRD PARTY ULTRA-WIDEBAND DEVICES TO ESTABLISHGEO-POSITIONAL DATA, Ser. No. 10/263,213, filed Aug. 28, 2002, which isa continuation-in-part of U.S. Pat. No. 6,519,464, titled: USE OF THIRDPARTY ULTRA-WIDEBAND DEVICES TO ESTABLISH GEO-POSITIONAL DATA, Ser. No.09/745,498, filed Dec. 22, 2000, which claims priority to U.S.Provisional patent application Ser. No. 60/255,469, filed Dec. 14, 2000,titled: ULTRA-WIDEBAND COMMUNICATION SYSTEM AND METHOD.

In the above-incorporated reference, an UWB device may determine itgeographical position based on the position of other UWB devices. Inthis embodiment, a first UWB device may send a position request messageto two, or more UWB devices that know their geographical location. Theother UWB devices would respond with a message that includes theirgeographical location. The first UWB device may then determine its owngeographical position based on the geographical location of theresponding UWB devices. Communication parameters may then be selectedbased on the distance between the UWB devices.

One embodiment of the present invention uses distance as one factor toselect various communications parameters. Other embodiments of thepresent invention may use a data bit-error-rate (BER) and/or a receivedsignal strength indicator (RSSI) as factors in selecting communicationparameters. In addition, one embodiment of the present invention may usethe derived distance information to designate “zones” that extendoutward from the UWB device. Sets of communication parameters may thenbe assigned for each zone.

However, UWB pulse, or signal propagation characteristics may varywithin each zone. As shown in FIG. 3, zones Z1, Z2, Z3 and Z4 emanateoutward from a UWB device (not shown) located at the center of zone Z1.For convenience of illustration, only four zones are illustrated,however embodiments of the present invention may have less than or morethan four zones.

One feature of the present invention enables more accurate selection ofcommunication parameters by partitioning each zone into discretesectors. Sectorization may be accomplished in a number of ways. In oneembodiment, sectors are assigned as portions of a circle measured indegrees. Shown in FIG. 3, a four-sector system, including sector 1,sector 2, sector 3 and sector 4 would comprise 90-degree portions ofeach zone Z1, Z2, Z3 and Z4. Depending upon the communicationsenvironment, and other factors, the number of sectors may be greaterthan, or less than the four illustrated sectors. Once zones and sectorsare established the UWB device selects various parameters to be used forinter-device communications based on the zone and sector of thedestination UWB device.

There are various communication parameters that may be employed toenable communication between UWB devices. These communication parametersmay include the UWB pulse modulation technique, the method of errordetection and correction, the error control algorithm, the UWB pulserecurrence frequency, the data rate, the power of transmission, the UWBpulse shape, the configuration of the receiver, the UWB pulse width, theframe length, the frequency of master time reference synchronization,and other suitable communication parameters.

Ultra-wideband pulse modulation techniques enable a singlerepresentative data symbol to represent a plurality of binary digits, orbits. This has the obvious advantage of increasing the data rate in acommunications system. A few examples of modulation include Pulse WidthModulation (PWM), Pulse Amplitude Modulation (PAM), and Pulse PositionModulation (PPM). In PWM, a series of predefined UWB pulse widths areused to represent different sets of bits. For example, in a systememploying 8 different UWB pulse widths, each symbol could represent oneof 8 combinations. This symbol would carry 3 bits of information. InPAM, predefined UWB pulse amplitudes are used to represent differentsets of bits. A system employing PAM16 would have 16 predefined UWBpulse amplitudes. This system would be able to carry 4 bits ofinformation per symbol. In a PPM system, predefined positions within anUWB pulse timeslot are used to carry a set of bits. A system employingPPM16 would be capable of carrying 4 bits of information per symbol.Additional UWB pulse modulation techniques may include: Coded RecurrenceModulation (CRM) as described in co-pending U.S. patent application,Ser. No. 10/294,021, titled “ULTRA-WIDEBAND PULSE MODULATION SYSTEM ANDMETHOD”; Sloped Amplitude Modulation (SLAM) as described in co-pendingU.S. patent application, Ser. No. 10/188,987, titled “ULTRA-WIDEBANDPULSE GENERATION SYSTEM AND METHOD”; ternary modulation, as described inco-pending U.S. patent application, Ser. No. to be assigned, filed Apr.28, 2003, titled “ULTRA-WIDEBAND PULSE MODULATION SYSTEM AND METHOD”,which claims priority to Provisional patent application Ser. No.60/452,020, of the same title; 1-pulse modulation, as described inco-pending U.S. patent application, Ser. No. to be assigned, filed Apr.29, 2003, titled “ULTRA-WIDEBAND PULSE MODULATION SYSTEM AND METHOD”;and other UWB pulse modulation methods as described in co-pending U.S.patent application, Ser. No. 09/710,065, titled “ULTRA-WIDEBANDCOMMUNICATION SYSTEM WITH AMPLITUDE MODULATION AND TIME MODULATION. Allof the above-listed non-provisional and provisional United States patentapplications are incorporated herein by reference in their entirety.

There are various methods of error detection and correction used incommunication systems. The simplest form of error detection involves theuse of a parity bit per block of data. The additional bit is set toensure that the block has either an even number of ones, if even parityis used, or an odd number of ones if odd parity is employed. Use ofparity will only detect an odd number of errors in a given block ofdata.

Another type of error detection is the Longitudinal Redundancy Check(LRC)/Vertical Redundancy Check (VRC) scheme. This method uses not onlyone parity bit per word, or row of the frame, considered now as amatrix, but also a “parity check character”, comprising the entire lastrow of the matrix, with each bit in the row checking the parity of thecorresponding column. The row parity bits form the last column and arecalled the VRC, while the column parity bits form the last row and arecalled the LRC or the parity check character. LRC/VRC will fail todetect conditions that have even number of errors in each column andeach row.

A common and powerful technique of error detection is CyclicalRedundancy Check (CRC). In CRC the transmitter generates a Frame CheckSequence (FCS) of a length necessary to ensure that when the FCS isappended to the block of bits the augmented block is divisible by apredetermined number. On receipt, the number of bits is divided by thepredetermined number, and if there is no remainder, the receiver assumesthat the message is error free. Any of the above-described errordetection methods, and other error detection methods not described, maybe employed by the present invention.

There are essentially two groups of error correction algorithms:Backward Error Correction (BEC) and Forward Error Correction (FEC). InBEC, also known as Reverse Error Correction (REC), the first devicesends a message, packet, or frame to a receiver. The second devicechecks the received data for error. If an error is detected, a requestto retransmit the message, packet, or frame is sent to the first device.In contrast, when using Forward Error Correction (FEC) the second devicecorrects the error without retransmission of data from the first device.BEC has the advantage of simplicity, but generally requires duplexcommunications channels. Additionally, since the first device isrequired to retransmit frames, the overall information throughput isreduced. FEC allows for one-sided communications, but can besignificantly more complex than BEC and can impose additional overheadin the data.

FEC algorithms are usually based on redundancy. The simplest form of FECis to repeat each data bit a number of times. The receiving device couldsimply vote on what the data bit should be based on the bits received.In general, “n” errors can be detected and corrected using this methodby repeating every bit 2n+1 times. There are numerous more complex FECalgorithms including, for example only, and not for limitation,Reed-Solomon coding, Viterbi coding, Turbo coding, and BCH coding. Inthe present invention, the methods of error detection and errorcorrection are communication parameters that an UWB enabled device canselect to optimize communication with other UWB devices.

There are various common error control algorithms that are used incommunication systems. Most of these algorithms are classified asautomatic repeat request (ARQ) algorithms. In some error control schemessuch as stop-and-wait ARQ, the receiving device responds to everymessage with either an acknowledgement (ACK) or with a negativeacknowledgement (NACK). The first device will not continue transmissionuntil either a NACK or an ACK is received from the second device. InGo-Back-N ARQ, the first device sends a number of frames and maintains asliding window of size N. If an error is detected in a frame, the seconddevice sends a NACK to the first device, and it discards all incomingframes until the erroneous frame is properly received. The first devicemust retransmit all frames from the one containing the error. Anothervariation on error control is Selective-Reject ARQ. In this algorithmthe second device processes the correct frames and sends a NACK to thefirst device. The first device is then required to resend only framesreceived in error. In the present invention, these and other errorcontrol methods may be communication parameters that an UWB enableddevice can employ to optimize communication with other UWB devices.

The ultra-wideband pulse recurrence frequency (PRF), or pulsetransmission rate, is an additional communication parameter that a UWBenabled device employing the methods of the present invention mayselect. The PRF may be selected to be fixed, or variable based on thetype or amount of data, or pseudo-random. Generally, a fixed PRF createsspectral lines at the PRF and its integer harmonics. This may beadvantageous when concentration of spectral energy is desired. Apseudo-random PRF spreads or “whitens” the spectrum occupied by the UWBcommunications. Using a pseudo-random PRF spreads the UWB energyrelatively evenly across the entire spectrum occupied. A variable PRFmay be additionally employed where the PRF is “hopped” periodicallybased on some other parameter, which may include but is not limited tothe data to be sent.

For example, in one embodiment of the present invention, an UWB devicemay select the data rate of a communication link based on distanceinformation, RSSI information, or other types of information. The datarate in a UWB pulsed communication system is usually calculated as theproduct of the PRF and the number of bits-per-symbol that the selectedmodulation technique encodes on the UWB pulse stream. When using avariable or pseudo-random PRF the data rate is generally dependent onthe effective PRF.

Another factor affecting communication quality and reliability is thebit-error-rate (BER), which is usually calculated as the ratio of badbits to good bits. Thus, the BER is a way to measure data transmissionintegrity. Generally, the BER is usually dependent on thesignal-to-noise ratio (SNR) at the receiver. One method to reduce BERand thereby improve the quality of service (QOS) is to improve the SNRby increasing the power of transmission of the UWB pulses, or signal. Inone embodiment of the present invention, an UWB enabled device mayselect the UWB signal transmission power level as a communicationparameter.

Another communication parameter that may be employed by the presentinvention is UWB pulse transmission power. Since Power Spectral Density(PSD) is the Fourier Transform of the autocorrelation function, and theshape of a UWB pulse affects the shape of the autocorrelation function,the specific shape of the transmitted UWB pulses impacts thedistribution of the UWB signal power in the spectrum occupied. Inenvironments where the transmitted power in certain frequencies islimited, UWB pulse shape is one method of controlling transmitted powerlevels. In one embodiment of the present invention, UWB pulse shape maybe a parameter that an UWB enabled device may select when communicatingwith other UWB enabled devices. For example, the UWB pulse shape maycomprise a Gaussian mono-cycle, a filtered substantially square pulse, apre-distorted pulse, a pulse with a predetermined phase, a pulse with apredetermined amplitude, and other suitable pulse shapes.

Multi-path effects is another factor that affects communication qualityand reliability. UWB pulses may be propagated over different paths,arriving at the intended receiver at different times, causing multi-pathinterference, or fading. One method of minimizing multi-path effects inwireless communication systems uses RAKE receivers. With a RAKEreceiver, a number of delayed copies of the signal are correlated andadded to the original signal to improve the SNR. The number of “fingers”in the receiver designates the number of delayed copies to be correlatedand summed. In one embodiment of the present invention, the number of“fingers” in the receiver may be a parameter that may be selected toimprove the quality and reliability of a communication system employingthe methods of the present invention.

Another communication parameter that may be employed by the presentinvention is UWB variable pulse widths, or durations. According to thescaling property of the Fourier Transform, as the UWB pulse timeduration or width increases, frequency content becomes more compact. Thetransmitted power for wide, or long duration UWB pulses in some casesmay rise above the noise floor, possibly interfering with conventionalRF signals. In one embodiment of the present invention, the powerspectral density of wider, or longer duration UWB pulses may becontrolled to ensure coexistence with conventional RF signals and toreduce distortion from the natural bandwidth of the channel.Additionally, wider, or longer duration UWB pulses contain more energy.For example, one embodiment of the present invention may employ UWBpulse widths, or durations that range from about 0.01 nanoseconds toabout 1 millisecond. In one embodiment of the present invention, UWBpulse width, or duration is a parameter that may be selected by an UWBenabled device to improve the quality and reliability of an UWBcommunication system.

Another communication parameter that may be employed by the presentinvention is UWB variable frame sizes, or lengths. A frame is a group oftime periods, or time bins into which UWB pulses may be placed. Theframe may include UWB pulses that provide information forsynchronization, carry data, aid in error correction, or contain othertypes of information, or provide other functions. Frame length and thefrequency of synchronization can additionally impact the BER andtherefore the QOS. Frames of long duration in a communication systemthat uses minimal synchronization frequency can suffer from increasedBER due to relative clock drift between UWB enabled devices. In oneembodiment of the present invention, frame length and the frequency ofsynchronization are parameters that may be selected, and varied by a UWBenabled device to improve the quality and reliability of an UWBcommunication system.

With reference to FIG. 3, one embodiment of an ultra-widebandcommunication system employing the methods described above may functionin the following way: a UWB device located at the center of zone Z1 maycommunicate with a UWB device located in zone Z2, sector 1, by employingReed-Solomon forward error correction, 16 level pulse amplitudemodulation, a Gaussian monocycle pulse shape, a fixed pulse recurrencefrequency of 100 MHz with an average power of 0.5 watts. The UWB devicemay select to process received communications from the remote UWB devicein zone Z2 using 3 fingers in a RAKE receiver.

The same UWB device located at the center of zone Z1, when communicatingwith another UWB device in zone Z4, sector 2, may select Viterbi forwarderror correction, 4 level pulse amplitude modulation with 4 level pulseposition modulation, a fixed pulse recurrence frequency of 75 MHz, anessentially rectangular pulse shape of 300 pico-second duration, and anaverage transmission power of one watt. The UWB device may select toprocess received communications from the UWB device in zone Z4 using 5fingers in a RAKE receiver.

Another feature of the present invention is that it provides a method ofsharing bandwidth between UWB enabled devices. In this embodiment, a UWBenabled device may route communications through other UWB enableddevices in order to achieve a reliable, and higher QOS communicationslink to the destination UWB enabled device. In one implementation ofthis embodiment, an UWB enabled device can obtain an estimation of theavailable bandwidth in the zones and sectors it has access to, andforward this information to other UWB enabled devices that it iscommunicating with. Thus, a first UWB device wishing to communicate witha second UWB device may establish either a direct communications linkwith the second UWB device, or alternatively route communications to thesecond UWB device through other UWB enabled devices, based on theprovided available bandwidth information.

In one embodiment of the present invention, one of the UWB enableddevices is a fixed network access point (FNAP). In this embodiment, theFNAP knows its own geo-position in three-dimensional space. On functionof the FNAP is to characterize the UWB communications environment withinits geo-position to all UWB enabled devices in its range. Thus, the FNAPestablishes preferred communications parameters with in its localcommunications environment and stores a channel model, a zonedesignation, and the communications parameters associated with isthree-dimensional coordinates. As a new UWB enabled device powers up, ormoves within range of the FNAP, the appropnate zone, three-dimensionalgeo-coordinates, and associated communications parameters are assignedto the new UWB enabled device by the FNAP.

A FNAP may be part of a larger UWB network, or may it may establish itsown network. As defined herein, a network is a group of points or nodesconnected by communication paths. The communication paths may beconnected by wires, or they may be wirelessly connected. A network asdefined herein can interconnect with other networks and containsubnetworks. A network as defined herein can be characterized in termsof a spatial distance, for example, such as a local area network (LAN),a personal area network (PAN), a metropolitan area network (MAN), a widearea network (WAN), and a wireless personal area network (WPAN), amongothers. A network as defined herein can also be characterized by thetype of data transmission technology in use on it, for example, a TCP/IPnetwork, and a Systems Network Architecture network, among others. Anetwork as defined herein can also be characterized by whether itcarries voice, data, or both kinds of signals. A network as definedherein can also be characterized by who can use the network, forexample, a public switched telephone network (PSTN), other types ofpublic networks, and a private network (such as within a single room orhome), among others. A network as defined herein can also becharacterized by the usual nature of its connections, for example, adial-up network, a switched network, a dedicated network, and anonswitched network, among others. A network as defined herein can alsobe characterized by the types of physical links that it employs, forexample, optical fiber, coaxial cable, a mix of both, unshielded twistedpair, shielded twisted pair, or a wireless medium, such as air.

One drawback of a network is the possibility of multi-user interference(MUI), which generally results from multiple UWB enabled devicescommunicating in a close geographical region. In one embodiment of thepresent invention, a fixed access point assigns time periods to eachzone for communication. In this embodiment, consecutive time periods areassigned to zones that may not be geographically contiguous. Thisassignment may be accomplished on a functional logic block (FLB) basisthat may be similar to a Time Division Multiple Access (TDMA) scheme.For example, in one embodiment of the present invention, a fixed accesspoint may divide its surrounding area into 4 concentric zones Z1, Z2, Z3and Z4, as shown in FIG. 3. A first FLB, FLB 1 may be assigned to UWBenabled devices within zone Z2, and a second FLB, FLB 2 may be assignedto devices within zone Z4, a third FLB, FLB 3 may be assigned to UWBenabled devices within zone Z1, and a fourth FLB, FLB 4 may be assignedto zone Z3. Alternatively, time slots within a FLB may be assigned tozones in a similar manner. Devices within each zone can access theassigned time period on either a contention basis, such as employed byALOHA, CSMA, or CSMA-CD schemes, or on a pre-assigned basis.

Referring to TABLE 1, one embodiment of the present invention comprisesa method for assignment of time periods available for transmitting UWBpulses within a UWB communications network. The time periods are madeavailable by first determining the number of zones within a geographicalarea. Once the number of zones is established, the number of FLBs, oralternatively, time slots within the FLBs are selected. Diversity, ornon-repetition in time period assignment is then created by firstcounting incrementally by the appropriate zone number, then eliminatingrepetition between the time bins assigned. For example, in one type ofsystem there may be eight zones (Z1-Z8), and the assignment repetitionrate may be 30. That is, 30 time bins are included within a frame (asdefined above, a frame is a group of time periods, or time bins intowhich UWB pulses may be placed), and each zone is allocated specifictime bins within the frame. Thus, each UWB device must only analyze thetime bins that are allocated to it, depending upon which zone the UWBdevice is located.

The first step of the assignment method of the present invention is tocount sequentially by zone number as shown in TABLE 1. TABLE 1 Zone TimePeriods Z1 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 Z2 1, 3, 5, 7, 9, 11,13, 15, 17, 19, 21, 23, 25, 27, 29 Z3 1, 4, 7, 10, 13, 17, 20, 23, 26,29 Z4 1, 5, 9, 13, 17, 21, 25, 29 Z5 1, 6, 11, 16, 21, 26 Z6 1, 7, 13,19, 25 Z7 1, 8, 15, 23, 30 Z8 1, 9, 17, 25

Following the initial assignment, duplicate time periods, or bins areeliminated. This can be accomplished in a number of ways. In thisexample, the elimination of duplicate time bins is accomplished from thehighest numerical zone (Z8) to the lowest numerical zone (Z1). In zoneZ8 there is an assignment of the 1, 9, 17, and 25 time bins. These timebins are eliminated in the frames used by UWB devices located in zonesZ1 through Z7, as shown below in TABLE 2. The remaining time binassignments for zone Z7 are then eliminated from zones Z1 through Z6 inthe same manner. This process is continued until all duplicity, orrepetition is removed from the time bin assignments. TABLE 2 shows theresult of this method of time bin assignments. TABLE 2 Zone Time PeriodsZ1 2, 12, 14, 18, 22, 24, 28 Z2 3, 27 Z3 4, 10, 20 Z4 5, 29 Z5 6, 11,16, 21, 26 Z6 7, 13, 19 Z7 8, 15, 23, 30 Z8 1, 9, 17, 25

In TABLE 2 it is seen that the distribution of FLBs or alternativelytime bins is not evenly distributed. The zones containing more timebins, or FLBs will have a higher bandwidth capacity than zones withfewer time bins, or FLBs. One feature of the present invention is thatzone allocation may be based on bandwidth demand. That is, zones may notbe geographically allocated (with a local UWB device at the center ofzone Z1), but instead they may be allocated so that higher bandwidthzones are allocated to areas that contain a dense population of UWBdevices, or to areas that have a high bandwidth demand. Thus, in oneembodiment of the present invention, a local UWB device may be locatedat the center of zone Z8.

Thus, one feature of the present invention is that it provides a method,system, computer software or logic and/or computer hardware forproviding a high QOS in an UWB communication system by providing dynamicbandwidth allocation. In one embodiment of the present invention, alocal UWB enabled device may assign zones based on a population densityof UWB devices within each zone, assigning zones that contain more timebins to areas that have a higher density of UWB devices. These zoneassignments may change, based on changes in bandwidth demand.Alternatively, the geographic configuration of the zones may change, sothat areas that have less UWB devices can be incorporated, or mergedinto other zones to create a zone with more users. Thus, this method ofbandwidth allocation may result in zones that are not circular, orspherical, but instead may have irregular shapes.

Referring to FIG. 3, one method of practicing the present invention isillustrated. A first UWB enabled device (not shown) is located at thecenter of zone Z1. Other UWB devices may be located in any of the otherzones Z1, Z2, Z3, and Z4. The first UWB device may obtain distance,RSSI, BER and other types of information relating to each of the otherUWB devices that are in communication with the first UWB device. Basedon the data received from the communicating UWB devices, zones Z1through Z4 and sectors 1 through 4 are established. The determination ofthe number of, and the size of, zones and sectors may be based ondistance data, on the density of RF signals, on other types ofinformation discussed above, or on a combination of types ofinformation.

When communicating with UWB devices, the first UWB device determines thezone and sector of the other UWB device. Based on the zone and sector,the first UWB device selects appropriate communications parameters forcommunication with the other UWB device. A UWB device may be a phone, apersonal digital assistant, a portable computer, a laptop computer, anynetwork as described above (LAN, WAN, PAN etc.), video monitors,computer monitors, or any other device employing UWB technology.

Referring to FIG. 4, one type of messaging used to establish distancebetween UWB enabled devices is displayed. A first UWB enabled devicebroadcasts a “time request message” to at least one other UWB enableddevice, that is time synchronized with the first UWB device by a mastertime reference. The “time request message” includes the time ofbroadcast, or transmission from the first UWB device. Other UWB enableddevice(s) can then determine the distance to the first UWB device bysubtracting the time that the “time request message” was received fromthe embedded transmission time contained in the “time request message.”The time difference is the propagation time, and because RF energygenerally propagates at approximately the speed of light, the distancebetween the communicating UWB devices may be determined.

In addition, the first UWB device can determine the distance to otherUWB device(s) by receiving a “time response message” that includes thecalculated propagation time from which the distance to the respondingUWB device can be determined. In an alternative embodiment, the UWBdevice may also independently verify the distance to the responding UWBdevice by subtracting the time that the “time response message” wasreceived from an embedded transmission time contained in the “timeresponse message.” In this embodiment, each UWB device includes thetransmission time in each message that is sent. Because all thecommunicating UWB devices are time synchronized to each other by amaster time reference, distance calculations based on time differencesare accurate.

Referring to FIG. 5 another method of practicing the present inventionis illustrated. This embodiment is another method of messaging used toestablish distance between UWB enabled devices. A first UWB enableddevice broadcasts a “distance request message” to at least one other UWBdevice, that is time synchronized with the first UWB device by a mastertime reference. The “distance request message” includes the time ofbroadcast, or transmission from the first UWB device. Other UWB enableddevice(s) receive the message, and also register the time that themessage was received. The receiving UWB device then determine thedistance to the first UWB device by subtracting the time that the“distance request message” was received from the embedded transmissiontime contained in the “time request message.”

In addition, the first UWB device can determine the distance to otherUWB device(s) by receiving a “distance response message” that includesthe distance calculated by the receiving UWB device. In this embodiment,the “distance response message” includes the distance and the time oftransmission of the “distance response message,” which is referenced tothe master time reference. The first UWB device can verify the distancefrom each responding UWB device by referencing the time of transmissionincluded in the “distance response message” with the time of arrival ofthe “distance response message.”

Referring to FIG. 6 another method of practicing the present inventionis illustrated. This embodiment is a method of messaging used todetermine the type of communication parameters for use between UWBenabled devices. A first UWB device broadcasts a “bit-error-rate (BER)request message” to at least one UWB enabled device. The “BER requestmessage” contains a predetermined sequence of symbols that all thecommunicating UWB have in computer memory, or in another suitablelocation. The sequence of symbols may be a representation of anarbitrary group of binary digits, such as “0101,” or “00110011,” or anyother desired group of symbols.

The receiving UWB device(s) receive the “BER request message,” anddetermine the bit-error-rate by comparison of the received symbols withthe predetermined sequence of symbols contained in computer memory. TheUWB device(s) then respond with a “BER response message” that includesthe calculated BER, and if a distance between the UWB devices is known,the probable BER to other UWB devices within a similar distance, orzone.

Referring to FIG. 7 another method of practicing the present inventionis illustrated. This embodiment is another method of messaging used todetermine the type of communication parameters for use between UWBenabled devices. A first UWB enabled device broadcasts a “fixed energyrequest message” at a predetermined energy level to at least one otherUWB enabled device. The other UWB enabled device(s) know thepredetermined energy level, as it may be contained in computer memory,or in another suitable location. The UWB device(s) receive the “fixedenergy request message”, and determine the received energy of the “fixedenergy request message,” comparing it with the predetermined energylevel. The difference is a received signal strength indicator (RSSI).The receiving UWB device(s) then respond with a “fixed energy responsemessage” that contains the RSSI. The first UWB device then receives the“fixed energy response message” containing the RSSI information, and maythen set the types of communication parameters for the communicating UWBdevices, based on the RSSI information.

An alternative embodiment of this method may have the first UWB devicecalculate its own RSSI by determining the energy level of the “fixedenergy response message” and compare it to the predetermined energylevel. In this way, changing communication conditions, such as movingUWB devices, or other variables can be accounted for. In thisembodiment, the “fixed energy response message” is broadcast at a fixedenergy level so that the first UWB device can determine the RSSI for the“fixed energy response messages” and compare it to the RSSI informationin those responses. By comparing the RSSI information, accuratecommunication parameters can be established.

Shown in FIG. 8 is an example of one embodiment of the presentinvention, where at least one of the remote UWB enabled devices is afixed UWB access point 100, such as an antenna, network node, or othersuitable device. The fixed access point 100 in this embodiment generatesthe master time reference for all the UWB devices that communicatewithin its range, or network. For example, each UWB device in range of,or communicating with the fixed access point 100 synchronizes itself inaccordance with the methods disclosed in co-pending U.S. patentapplication, Ser. No. 09/805,735, filed Mar. 13, 2001, titled:MAINTAINING A GLOBAL TIME REFERENCE AMONG A GROUP OF NETWORKED DEVICES,which is, and has been, incorporated herein by reference in itsentirety. Additionally, the fixed access point 100 may or may not assignzones and sectors to the UWB enabled devices within its range, ornetwork.

Referring now to FIG. 9, one embodiment of an ultra-wideband (UWB)communication network is illustrated. The fixed access point 100provides a communications link, and a master time reference to UWBdevices D1, D2, D3, and P1. The UWB devices D1, D2, D3, P1 maycommunicate directly with the fixed access point 100, as shown bydevices D3 and P1, or within their own network as shown by D1, D2, andD3. Additionally, the UWB device P1 may communicate directly with theUWB device D1 that is involved in communications with devices D2, andD3, which is communicating with the fixed access point 100. In oneembodiment of the present invention, as shown in FIG. 9, communicationsbetween UWB device D1 and the fixed access point 100 may be routedthrough UWB device D3 or P1. Alternatively, based on zone and sectorassignment, and/or based on other communications parameters, device D1may establish a direct communications link with fixed access point 100.

Referring now to FIG. 10, another embodiment of an ultra-wideband (UWB)communication network is illustrated. In this embodiment, UWB devicesP1, P2, P3, D1, D2, D3 may not be within range of a fixed access point100 as shown in FIGS. 8-9 to establish a communication network throughthe fixed access point 100. In this embodiment of the present invention,UWB enabled devices P1, P2, P3, and D1, D2, D3 are shown communicatingwithin their own respective networks. These networks may be private,and/or secure, or they may be accessible by other UWB devices. In thisembodiment, a mobile UWB enabled device Q1 can function as a fixedaccess point 100, assigning zones and sectors, and establishing a mastertime reference to the UWB devices within its range, or network.Alternatively, each UWB enabled device P1, P2, P3, D1, D2, D3 mayestablish its own zones and sectors for enabling reliable communicationto other UWB enabled devices. In addition, routing of communicationsbetween UWB devices may be through any available path, as shown in FIG.10, where device P3 and device D1 communicate through UWB device Q1, orUWB devices P3 and D1 may establish a direct communications link. Inthis embodiment, time synchronization between networks of devices may beachieved in accordance with the methods described in co-pending U.S.patent application, Ser. No. 09/805,735, filed Mar. 13, 2001, titled:MAINTAINING A GLOBAL TIME REFERENCE AMONG A GROUP OF NETWORKED DEVICES,which is, and has been, incorporated herein by reference in itsentirety.

Referring now to FIG. 11, spatial diversity is achieved and hencemulti-user interference (MUI) is reduced by the assignment of FLBs, oralternatively time bins within FLBs, to different geographical zones. Inthis embodiment of the present invention, a UWB enabled device (notshown) establishes zones 1102 (Z1, Z2, Z3, and Z4). In communicationwith other UWB devices within each zone Z1, Z2, Z3, Z4, the UWB enableddevice may use the following FLB or time bin 1101 assignment: FLB1101(1) may be used to communicate with UWB devices within zone Z3; FLB1101(2) may be used to communicate with UWB devices within zone Z1; FLB1101(3) may be used to communicate with UWB devices within zone Z4; andFLB 1101(4) may be used to communicate with UWB devices within zone Z2.In this embodiment, the FLB, or time bin assignment pattern is thenrepeated for subsequent communications.

Thus, it is seen that various ultra-wideband wireless communicationmethods are provided. One skilled in the art will appreciate that thepresent invention can be practiced by other than the above-describedembodiments, which are presented in this description for purposes ofillustration and not of limitation. The description and examples setforth in this specification and associated drawings only set forthpreferred embodiment(s) of the present invention. The specification anddrawings are not intended to limit the exclusionary scope of this patentdocument. Many designs other than the above described embodiments willfall within the literal and/or legal scope of the following claims, andthe present invention is limited only by the claims that follow. It isnoted that various equivalents for the particular embodiments discussedin this description may practice the invention as well.

1. A method of selecting at least one communication parameter in anultra-wideband communication system based on a geographical area, themethod comprising the steps of: providing an ultra-wideband device;establishing a plurality of geographical areas, with the ultra-widebanddevice located substantially at a center of one of the geographicalareas; and assigning at least one communication parameter to eachgeographical area.
 2. The method of claim 1, wherein a similarcommunication parameter is assigned to each geographical area, but acharacteristic of the similar communication parameter varies based oneach geographical area.
 3. The method of claim 2, wherein the similarcommunication parameter is selected from at least one of a groupconsisting of: an ultra-wideband pulse modulation technique, a method oferror detection, a method of error correction, a method of errorcontrol, a ultra-wideband pulse recurrence frequency, an ultra-widebandpulse shape, a frame length, and a rate of time synchronization.
 4. Themethod of claim 2, wherein the characteristic of the similarcommunication parameter communication parameter is selected from atleast one of a group consisting of: a data rate, a power oftransmission, a configuration of a receiver, and an ultra-wideband pulsewidth.
 5. The method of claim 1, wherein the geographical areas areestablished by a distance between the ultra-wideband device and anotherultra-wideband device.
 6. A method of selecting at least onecommunication parameter in an ultra-wideband communication system, themethod comprising the steps of: providing a first ultra-wideband deviceand a second ultra-wideband device; determining a distance between thefirst ultra-wideband device and the second ultra-wideband device;establishing a plurality of geographical areas, with at least one of theultra-wideband devices located substantially at a center of one of thegeographical areas; partitioning each of the geographical areas into atleast two sectors; and assigning at least one communication parameter toeach geographical area and to each sector.
 7. The method of claim 6,wherein the communication parameter is selected from at least one of agroup consisting of: an ultra-wideband pulse modulation technique, amethod of error detection, a method of error correction, a method oferror control, a ultra-wideband pulse recurrence frequency, a data rate,a power of transmission, an ultra-wideband pulse shape, a configurationof a receiver, an ultra-wideband pulse width, a frame length, and a rateof time synchronization.
 8. The method of claim 6, wherein the secondultra-wideband device transmits the distance, geographic area and sectorto the first ultra-wideband device.
 9. A method of providing spatialdiversity in an ultra-wideband communication system, the methodcomprising the steps of: providing a first ultra-wideband device and asecond ultra-wideband device; establishing a plurality of geographicalareas, with at least one of the ultra-wideband devices located in afirst geographical area, and the second ultra-wideband device located ina second geographical area; using a group of ultra-wideband time periodsto communicate between the first ultra-wideband device and the secondultra-wideband device; and assigning specific time periods to each ofthe geographical areas.
 10. The method of claim 9, wherein the step ofassigning specific time periods to each of the geographical areascomprises the steps of: selecting a repetition interval for the group ofultra-wideband time periods; assigning to each geographic area at leastone time period; and eliminating repetitive time periods from eachgeographic area.
 11. A method of selecting at least one communicationparameter in an ultra-wideband communication system based on a distance,the method comprising the steps of: providing a first ultra-widebanddevice; transmitting a geographical location request message from thefirst ultra-wideband device to at least two ultra-wideband deviceshaving known geographical locations; receiving a response message fromthe at least two ultra-wideband devices, the response message includingthe geographical location of each of the at least two ultra-widebanddevices; calculating the distance between the first ultra-widebanddevice and the at least two ultra-wideband devices; and selecting atleast one communication parameter based on the calculated distance. 12.The method of claim 11, wherein the at least one communication parameteris selected from at least one of a group consisting of: anultra-wideband pulse modulation technique, a method of error detection,a method of error correction, a method of error control, aultra-wideband pulse recurrence frequency, an ultra-wideband pulseshape, a frame length, a rate of time synchronization, a data rate, apower of transmission, a configuration of a receiver, and anultra-wideband pulse width.